Mixed fuel suitable for diesel engines

ABSTRACT

The present invention a mixed fuel suitable for diesel engines, which consists of the following components by volume percentage: 35% to 37.5% of diesel, 35% to 37.5% of ethanol and 25% to 30% of PODE, wherein the diesel is petroleum diesel having a cetane number not less than 48; the purity of the ethanol by mass percentage is not less than 99.5%; and, the PODE is a mixture of two fuels shown by molecular formulae CH3O(CH2O)3CH3 and CH3O(CH2O)4CH3. The use of this fuel is advantageous for emission reduction.

TECHNICAL FIELD

The present invention relates to the technical field of clean energy for internal combustion engines, and in particular to a mixed fuel suitable for diesel engines.

BACKGROUND OF THE PRESENT INVENTION

The automobile ownership in China has increased from 77 million in 2010 to 184 million in 2016. With the rapid growth of automobile ownership, the consumption of petroleum resources is increasing, and the environmental pollution is increasingly serious. Seeking a renewable and clean fuel is the key to effectively solve the shortage of petroleum resources and the serious environment pollution currently.

Due to high heat efficiency and excellent dynamic performance and reliability, internal combustion engines are widely applied in various fields such as automobiles, agricultural machinery and engineering machinery. In the foreseeable future, internal combustion engines will become a prime mover for transportation machinery. Compared with gasoline engines, diesel engines have higher heat efficiency, which is advantageous for energy conservation and CO₂ emission reduction. However, for conventional diesel engines, since the diesel fuel can be combusted quickly after injected into a cylinder due to its low volatility and good ignitability, it is unable to fully mix the fuel with air, resulting in the formation of soot in a local over-concentrated area. The high carbon smoke and high NO_(x) emission of the diesel engines are existing problems to be solved.

Ethanol, belongs to a renewable energy source, is mainly prepared from biological materials rich in starch and carbohydrate through fermentation, distillation and purification. Due to its abundant raw material sources such as corn, sugar cane and biomass wastes, ethanol has become the most widely used biomass fuel in the world. If ethanol is mixed with diesel, the non-renewable diesel is partially replaced with the renewable ethanol fuel, so the shortage of petroleum resources is solved. Further, since ethanol has good volatility, the problem that diesel cannot be fully mixed with air can be overcome, and the soot emission can be reduced. Moreover, the oxygen content of the ethanol fuel can further reduce the soot emission. Additionally, the ethanol fuel has large latent heat of vaporization, the temperature in the cylinder can be effectively lowered, and the NO_(x) emission can be thus reduced. Therefore, by mixing ethanol with diesel, the shortage of energy sources can be effectively solved, and the emission can be reduced.

The diesel and the ethanol cannot be completely mixed with each other under normal conditions due to their differences in hydrocarbon composition and polarity. Therefore, the study on miscibility of ethanol and diesel is a basis for the practical applications of diesel/ethanol mixed fuel. In addition, the cetane number is an index for indicating the ignitability of the fuel, since the cetane number of ethanol is only about 8, the overall cetane number of the diesel/ethanol mixed fuel is low. As the mixing ratio of the ethanol increases, the overall cetane number decreases, so that the ignitability is obviously lower than that of the diesel. This will result in an excessive pressure drop rate at a low load and the increase of emissions such as CO, HC and NOx. Therefore, the cosolvent can realize the effective mixing of diesel and ethanol, and also has a certain cetane number to ensure the ignitability of the diesel/ethanol mixed fuel.

Although the addition of high-carbon alcohols in the diesel/ethanol mixed fuel can effectively solve the fuel stratification problem, the high-carbon alcohols cannot satisfy the requirements for the cetane number due to their low cetane number. The addition of biodiesel can solve the problem on miscibility of the diesel/ethanol mixed fuel and have a cetane number equivalent to that of the biodiesel. Therefore, the addition of biodiesel is advantageous for increase the overall cetane number. Moreover, the biodiesel has certain oxygen content, it is advantageous for emission reduction. However, the biodiesel produced by using rapeseed oil as raw material is expensive but the biodiesel synthesized by chemical methods is prone to deteriorate, so the biodiesel is also not a desired cosolvent.

SUMMARY OF THE PRESENT INVENTION

The objective of the present invention is to overcome the deficiencies of the prior art and provide a mixed fuel suitable for diesel engines which is advantageous for emission reduction.

A mixed fuel suitable for diesel engines, consisting of the following components by volume percentage:

35% to 37.5% of diesel, 35% to 37.5% of ethanol and 25% to 30% of PODE;

the diesel is petroleum diesel having a cetane number not less than 48;

the purity of the ethanol by mass percentage is not less than 99.5%; and

the PODE is a mixture of two fuels shown by molecular formulae CH₃O(CH₂O)₃CH₃ and CH₃O(CH₂O)₄CH₃.

The mixed fuel suitable for diesel engines in the present invention has the following advantages.

1. The PODE has a high cetane number of about 60 and a very high oxygen content of about 50%. The PODE can increase the overall cetane number of the mixed fuel, and can effectively reduce emission due to its high oxygen content. In addition, compared with other cosolvents (such as, high-carbon alcohols that cannot regulate the cetane number, and biodiesel oil that is expensive and unstable and easy to be oxidized and deteriorated at a high temperature), the PODE, acts as a cosolvent, effectively solves the problem that the diesel and the ethanol are not completely miscible, and can well solve the existing problems of the high-carbon alcohols and biodiesel oil. As a renewable energy source, the PODE has a wide range of raw material sources and high generalization performance, so the dependency on petroleum resources can be reduced to a certain extent.

A novel mixed fuel of diesel/ethanol/PODE is prepared by adding PODE into a wide-distillate fuel of diesel and ethanol, and the cetane number of the mixed fuel is close to that of diesel by rationally controlling the proportion of the three fuels. This fuel is moderate in ignitability and can stably combust in a diesel engine. Due to the high oxygen content of the PODE fuel, the emissions of soot, CO and HC of the diesel engine are significantly reduced.

2. The use of the ethanol fuel as a renewable energy source can overcome the heavy dependency on petroleum resources to a certain extent. Due to the high volatility of ethanol, the oil-gas mixing process before ignition can be accelerated; and, the oxygen content of ethanol also facilitates the emission reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the miscibility of diesel and ethanol at different temperatures;

FIG. 2 shows the miscibility of diesel/ethanol/PODE in different proportions under the temperature of 20° C.; and

FIG. 3 shows the miscibility of diesel/ethanol/PODE in different proportions under the temperature of 30° C.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The following implementations are used for describing the present invention, rather than limiting the scope of the present invention.

The present invention provides a mixed fuel suitable for diesel engines, which consists of the following components by volume percentage:

35% to 37.5% of diesel, 35% to 37.5% of ethanol and 25% to 30% of PODE.

The diesel is petroleum diesel having a cetane number not less than 48 and is commercially available. The purity of the ethanol by mass percentage is not less than 99.5%.

The PODE is a mixture of two fuels shown by molecular formulae CH₃O(CH₂O)₃CH₃ and CH₃O(CH₂O)₄CH₃.

Preferably, the volume percentage of the fuel shown by the molecular formula CH₃O(CH₂O)₃CH₃ in the PODE is 50% to 80%.

Preferably, the mixed fuel consists of the following components by volume percentage: 36% of diesel, 36% of ethanol and 28% of PODE.

Preferably, the content of sulfur in the diesel is less than 10 ppm. It can be seen from FIG. 1 that, when the ethanol proportion of the mixed fuel is 10% to 90%, the miscibility of diesel and ethanol cannot be realized at the normal temperature of 25° C. and can only be realized at a high temperature, but the ambient temperature often cannot reach the miscibility temperature. However, it can be seen from FIGS. 2 and 3 that there are a miscibility area above the curve and a layering area below the curve and the miscibility of diesel/ethanol can be realized at a low temperature by titrating the PODE. Under the temperature of 20° C., the miscibility of diesel/ethanol can be realized by at most 26% of PODE by volume percentage; and, under the temperature of 30° C., the miscibility of diesel/ethanol can be realized by at most 13% by volume percentage.

Apparently, the respective proportion of the diesel/ethanol/PODE needs to satisfy the miscibility principle.

A method for preparing the fuel of the present invention includes the following steps of: preparing the components in volume proportion, adding ethanol in the diesel to form a mixed solution of incomplete mutual solubility, adding PODE in the mixed solution while stirring, and mixing uniformly to obtain a mixed fuel.

The cetane number of the mixed fuel provided by the present invention is within the range from 45 to 55.

In the mixed fuel provided by the present invention, the diesel/ethanol/PODE has good miscibility, so the mixed fuel can be stored for a long term without layering.

Embodiment 1

The mixed fuel consists of 37.5 L of diesel, 37.5 L of ethanol and 25 L of PODE.

The diesel is petroleum diesel having a cetane number not less than 48. The purity of the ethanol by mass percentage is 99.5%.

The PODE is a mixture of two fuels shown by molecular formulae CH₃O(CH₂O)₃CH₃ and CH₃O(CH₂O)₄CH₃.

The volume percentage of the fuel shown by the molecular formula CH₃O(CH₂O)₃CH₃ in the PODE is 50%.

The content of sulfur in the diesel is less than 10 ppm.

The method for preparing the fuel of the embodiment 1 of the present invention includes the following steps of: preparing the components in volume proportion, adding ethanol in the diesel to form a mixed solution of incomplete mutual solubility, adding PODE in the mixed solution while stirring, and mixing uniformly to obtain a mixed fuel. The preparation methods in the following embodiments are the same as that in Embodiment 1.

Embodiment 2

The mixed fuel consists of 37 L of diesel, 37 L of ethanol and 26 L of PODE.

The diesel is petroleum diesel having a cetane number not less than 48. The purity of the ethanol by mass percentage is 99.5%.

The PODE is a mixture of two fuels shown by molecular formulae CH₃O(CH₂O)₃CH₃ and CH₃O(CH₂O)₄CH₃.

The volume percentage of the fuel shown by the molecular formula CH₃O(CH₂O)₃CH₃ in the PODE is 60%.

The content of sulfur in the diesel is less than 10 ppm.

Embodiment 3

The mixed fuel consists of 36.5 L of diesel, 36.5 L of ethanol and 27 L of PODE.

The diesel is petroleum diesel oil having a cetane number not less than 48. The purity of the ethanol by mass percentage is 99.5%.

The PODE is a mixture of two fuels shown by molecular formulae CH₃O(CH₂O)₃CH₃ and CH₃O(CH₂O)₄CH₃.

The volume percentage of the fuel shown by the molecular formula CH₃O(CH₂O)₃CH₃ in the PODE is 70%.

The content of sulfur in the diesel is less than 10 ppm.

Embodiment 4

The mixed fuel consists of 36 L of diesel, 36 L of ethanol and 28 L of PODE.

The diesel is petroleum diesel having a cetane number not less than 48. The purity of the ethanol by mass percentage is 99.5%.

The PODE is a mixture of two fuels shown by molecular formulae CH₃O(CH₂O)₃CH₃ and CH₃O(CH₂O)₄CH₃.

The volume percentage of the fuel shown by the molecular formula CH₃O(CH₂O)₃CH₃ in the PODE is 80%.

The content of sulfur in the diesel is less than 10 ppm.

Embodiment 5

The mixed fuel consists of 35 L of diesel, 35 L of ethanol and 30 L of PODE.

The diesel is petroleum diesel having a cetane number not less than 48. The purity of the ethanol by mass percentage is 99.5%. The PODE is a mixture of two fuels shown by molecular formulae CH₃O(CH₂O)₃CH₃ and CH₃O(CH₂O)₄CH₃.

The volume percentage of the fuel shown by the molecular formula CH₃O(CH₂O)₃CH₃ in the PODE is 65%.

The content of sulfur in the diesel is less than 10 ppm.

When the four mixed fuels obtained in Embodiments 1 to 5 are tested by a heavy-duty diesel engine having a displacement of 8.42 L, the results indicate that the smoke emission of the novel mixed fuel provided by the present invention is obviously lower (above 50%) than that of the diesel or the mixed fuel of diesel/PODEn and the emission of CO and THC is reduced to different extents.

The foregoing embodiments are merely preferred implementations of the present application and not intended to limit the scope of the present application. Various transformations and improvements made to the technical solutions of the present invention by a person of ordinary skill in the art without departing from the design spirit of the present invention shall fall into the protection scope defined by the appended claims of the present application. 

1. A mixed fuel suitable for diesel engines, consisting of the following components by volume percentage: 35% to 37.5% of diesel, 35% to 37.5% of ethanol and 25% to 30% of PODE; the diesel is petroleum diesel having a cetane number not less than 48; the purity of the ethanol by mass percentage is not less than 99.5%; and the PODE is a mixture of two fuels shown by molecular formulae CH₃O(CH₂O)₃CH₃ and CH₃O(CH₂O)₄CH₃.
 2. The mixed fuel suitable for diesel engines according to claim 1, wherein the volume percentage of the fuel shown by the molecular formula CH₃O(CH₂O)₃CH₃ in the PODE is 50% to 80%.
 3. The mixed fuel suitable for diesel engines according to claim 1 or 2, wherein the mixed fuel consists of the following components by volume percentage: 36% of diesel, 36% of ethanol and 28% of PODE.
 4. The mixed fuel suitable for diesel engines according to claim 3, wherein the content of sulfur in the diesel is less than 10 ppm. 